The present invention generally relates to a rotary machine, and more particularly, to a rotor of a rotary machine with permanent magnets, which includes an iron core in a position close to its inner diameter, and permanent magnets disposed therearound.
Generally, a rotor of a rotary machine with permanent magnets not provided with a starting winding is so constructed that, with an iron core portion disposed inside, permanent magnets are arranged at an outer side thereof so as to increase the magnet area.
For efficiently producing the rotor having such a construction, there has often been adopted a practice as disclosed, for example in Japanese Laid-Open Patent Publication Tokkaisho No. 58-151855, in which, with a plurality of magnets each having an arcuate cross section being disposed inside a cylindrical cover member, laminated iron plates having an opening for passing molten metal therethrough during die-casting are further disposed within the portion surrounded by said plurality of magnets, and thereafter, molds each having an annular space communicated with said opening of the laminated iron plates are applied onto opposite end faces for die-casting.
In the prior art as disclosed in the Tokkaisho No. 58-151855 referred to above, however, since the die-casting is required, not only is the installation cost increased, but dimensional accuracy for an inner diameter of the laminated iron core and an outer diameter of the cylindrical cover is undesirably deteriorated by heat and pressure during pouring of the molten metal, thus requiring cutting processing after the die-casting.
In order to overcome the disadvantages as described above, there has recently been proposed a rotor for a rotary machine with permanent magnets having the construction as shown in FIGS. 5 and 6. In the above prior art arrangement, a plurality of magnets 2 each having an arcuate cross section are disposed around an outer periphery of a cylindrical laminated iron plate core 1, and a non-magnetic metallic pipe 3 is forcibly applied over the outer peripheries of said plurality of magnets 2, thereby to dispense with the die-casting. As shown in FIGS. 7(a) and 7(b), and FIG. 8, each of the magnets 2 having the arcuate cross section is formed, at one end portion (or both end portions) on its outer circumferential face in an axial direction thereof, with chamfering 4a of a uniform width and directed to be parallel with said one end portion (or said both end portions).
However, in the prior art rotor as described above, during application of the non-magnetic metallic pipe 3 over the outer peripheries of the magnets 2 under pressure, there have been many cases where the pipe 3 can not withstand the pressure for the application, with seizure as indicated by arrows 6 in the inner periphery of said pipe 3 or collapsing 7 of said pipe 3 taking place as shown in FIGS. 9 and 10, thus resulting in the faulty products. Such a defect is attributable to the fact that distribution of the pressure (indicated by arrows 5 (FIG. 11(b)) on the contact surfaces between the pipe 3 and the permanent magnets 2 at the moment of forcible application of the pipe 3 over the magnets 2 is concentrated at portions between the neighboring permanent magnets 2 as shown in FIGS. 11(a) and 11(b).